I Just went through this myself. I called up Nick Micale, and he sent me a set of his VS739R valve springs which was also suggested by Mike Kurtz who installed them at his shop in Richmond, TX. These springs are both readily available, and inexpensive. Noticeably improved power a bit down low, and on the top end. Otherwise the car retains the stock valvetrain cam etc.Put it in the oven?
This is a goofy suggestion. The springs are heat-treated and tempered at the factory (that's what makes them springs, as opposed to a coil of wire that crushes the first time you compress it), and you need to get steel a lot hotter than you'll find on top of a head to do anything to the metal.